1. Field of the Invention
This invention relates generally to communications systems and, more particularly, to a device and method for determining characteristics of an existing wire network to determine the suitability of the wire network for use with various data transmission technologies.
2. Description of the Related Art
Over the last few years, the demand for high speed communication applications has exploded. The Internet, for example, has grown at astronomical rates over the past several years. A significant number of new Internet subscribers connect from a home or small office using a personal computer (PC). One drawback typically associated with home and small office Internet connections is the relatively slow speeds at which data is transferred between the Internet service provider and the subscriber's PC.
The relatively low data transfer speeds associated with home, PC-based Internet connections are primarily the result of the low-bandwidth capabilities of the wiring used to connect the PC to the Internet service provider. More particularly, a data “bottleneck” is introduced by the copper wiring used to connect the central office (CO) of the telephone company to the home.
Until recently, few options have been available to the home or small business user to increase the data transfer bandwidth. Users could purchase expensive, dedicated T-1 or frame relay lines that have relatively high bandwidths (e.g., 1.5 Mbps). The cost of such lines, however, are prohibitive for most home uses. Accordingly, most telecommuters, mobile users, and small office/home office (SOHO) users must use a lower bandwidth data transfer technology such as 56 kbps asynchronous modem connections, integrated services digital networks (ISDN), and the like.
One suggestion to increase the bandwidth for home uses is to provide high bandwidth lines (e.g., optical cabling) directly to the home. Such an approach is very expensive since extremely large amounts of new optical cabling or wiring must be installed. Such an approach also ignores the value of the existing copper infrastructure already in place around the world. The existing copper networks have an undepreciated world-wide value estimated at over 600 billion dollars. There are approximately 700 million existing local copper loops around the world, and over 160 million in the United States. The principle difficulty in exploiting the copper wiring infrastructure is the traditionally low bandwidth data transmission capability of the twisted-pair copper wiring local loop that form the final link between the CO and the home.
Recently, digital subscriber line (xDSL) technologies have been developed to provide high-speed data transmission from the service provider (e.g., the CO) to the customer premise over the existing twisted-pair copper wiring conventionally used for telephone service. Such xDSL technologies leverage modem technology to increase the data transfer bandwidth of the twisted-pair copper wiring. Typically, xDSL modems are provided on the ends of the subscriber line copper wiring to communicate between the CO and the customer's premise. The manner in which the two modems communicate is established by the particular xDSL approach used. Because the existing telephone wire is used, xDSL technologies data signals are typically transferred out-of band with the voice band signals. Because different frequencies are used for the voice band and the data band, voice and data information can be concurrently transferred over the twisted-pair copper line. In a typical xDSL example, voice information may be carried in frequency bands below 4 kHz with data being carried in frequencies above the voice band, typically from 50 kHz to 1 MHz.
While xDSL technologies may be implemented in a number of different forms, each approach typically uses an xDSL model at the customer premise that communicates with an xDSL modem at the CO of the telephone company. At the CO, data transmitted over the subscriber line using xDSL technologies is communicated to Internet or other intranet services, for example, over high-speed wide area network (WAN) services, such as frame relay or ATM services. Different competing forms of digital subscriber line technologies are collectively designated as xDSL technologies where the “x” represents various one or more letter combinations that are used in front of the “DSL” acronym in order to designate the type of technology being used. Some of the more prevalent xDSL technologies currently being considered include HDSL, ADSL, SDSL and VDSL. To facilitate a better understanding of xDSL technology, a brief discussion of some of the differences between a few examples is set out below.
HDSL (High Data-rate Digital Subscriber Line) has been used as a low-cost substitute for Ti lines in symmetrical business-oriented wide area network (WAN) applications. HDSL typically supports 768 kbps full-duplex communication over a single twisted pair, T-1-speeds over two twisted pairs, and E2 speeds over 3 pairs. SDSL (Single-line Digital Subscriber Line) is well suited for home use or other small subscriber premises and provides T-1 or E1 date transmission speeds over a single twisted-pair copper line. SDSL supports standard voice band data transmissions and T-1/E-1 data band transmission simultaneously over the same line. ADSL (Asymmetric Digital Subscriber Line) exploits asymmetric upstream and downstream data transmission rates to increase the amount of data that may be delivered to the subscriber's premise. ADSL allocates the larger portion of the bandwidth to downstream traffic, providing rates ranging from Ti to 9 Mbps downstream and 16 to 640 kbps upstream. ADSL technologies typically use either carrierless amplitude-phase (CAP) modulation or discrete multitone (DMT) modulation techniques. ADSL technology is especially suited for connecting to a customer premise where, as is often the case in Internet applications, a significantly larger portion of data transfers are provided from the service provider to the customer premise than from the customer premise to the service provider.
A number of factors effect the data transmission rates that can be used. For example, the rate depends on the length and gauge of the twisted-pair copper line used for transmission. Table 1 lists exemplary lines widths and downstream data transmission rates using ADSL technology on a typical 24-gauge twisted-pair copper subscriber line.
TABLE 1Line LengthDown Stream Data Rate18,000 feet1.544 Mbps (T1)16,000 feet2.048 Mbps (E1)12,000 feet6.312 Mbps (DS2) 9,000 feet8.448 Mbps (E2)
As will be appreciated from the above-description, a number of different technologies may be used to transmit data over existing twisted-pair lines. The various technologies range, for example, from voice band modems having transmission speeds as low as 1,200 bps up to VDSL out-of-band technologies having downstream data transmission speeds from 13 to 52 Mbps. The ability to use the various schemes depends on a number of factors including, for example, the twisted-pair copper wiring length and gauge and overall structure of the wiring. As a result not all technologies can be used on a given digital subscriber line. It is difficult to determine which, if any, data scheme would be appropriate for a particular subscriber. Moreover, the characteristics of the line may change with time.
Another variable affecting the suitability of a particular customer premise is the specific telephonic and computer related equipment coupled to the copper network within the customer premise. Telephonic devices typically operate in one of two states, a high-impedance on-hook state and a lower impedance off-hook state. A ringing signal sent over the subscriber line to activate the telephonic devices is typically on the order of 100–200 volts. Typical telephonic devices include protective circuitry adapted to dissipate transient energy (e.g., due to line faults, lightning, etc.) encountered on the subscriber line to prevent damage to its internal components. The particular points at which such protective circuitry activates varies widely among the various telephonic devices available. Out-of-band transmission protocols, under certain conditions, have been found to inadvertently activate these protective circuits. These characteristics of the telephonic devices are referred to as non-linear characteristics. The non-linear characteristics may deleteriously affect or limit the use of out-of-band transmission schemes at the customer premise. Due to the widely distributed, non-standardized responses of the telephonic devices, it has proven extremely difficult to establish a model of the non-linear characteristics.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.